1. Field of the Invention
The present invention relates to a secondary cell in which charging and discharging are performed by utilizing the absorbing and releasing oxygen or inserting and eliminating oxygen ion.
2. Discussion of the Background
In recent years, accompanying the rapid popularization of information related devices, communication related devices and the like such as a personal computer, a video camera, a portable telephone and the like, the development of a secondary cell which is excellent for their electric sources has been considered as being important. Moreover, for the other fields in addition to the above-described information related devices and communication related devices, for example, also in the automotive industry, the development of a secondary cell having a high output and a high capacity for use in an electric automobile and a hybrid automobile as a low pollution vehicle has been proceeded. Furthermore, for the purpose of the leveling of electric power load due to the power generation and its power storage during night when electric power load is low, and also for the purpose of the storage of electric power derived from the natural energies such as a solar cell, the electric generation by wind power and the like which are varied by the climate and meteorological circumstances, the utilization of a secondary cell has been considered, and the development of a large scale secondary cell has been a task.
In such a background, in recent years, a secondary cell has been required to have a high performance, a long life span, a lower cost and the like. Then, as a secondary cell fulfilling such requirements, at present, a lithium ion secondary cell in which the insertion and elimination of lithium ion on the positive electrode and negative electrode are utilized for charging and discharging is considered as being the most promising secondary cell.
Moreover, the lithium ion secondary cell is characterized in that it can be made into an all-solid-state secondary cell by employing an ion conductive solid as an electrolyte (see patent documents 1–5 and non-patent document 1).
Thus, the liquid leakage and the like are eliminated and the safety is enhanced by thus making the lithium ion secondary cell into an all-solid-state secondary cell. Moreover, since the charge and discharge of the cell occur only by the simple reaction, and a side reaction does not occur, the longer life span of the cell can be expected.
Now, a secondary cell in which the insertion and elimination of the substances except for lithium ion are utilized for charging and discharging of the cell has been also considered. As such a secondary cell, for example, there is a secondary cell in which the insertion and elimination of fluoride ion are utilized (see patent document 6 and non-patent document 2). Moreover, a cell system in which the insertion and elimination of magnesium ion are utilized has been proposed (see patent document 7 and non-patent document 3). Moreover, a Nickel hydrogen cell which is commercially available in the market can be also considered as a cell in which the insertion and elimination of H+ are utilized.
In this way, up to this time, as a secondary cell, cells in which the insertion and elimination of Li+, F−, Mg2+ and H+ are utilized for charging and discharging have been in practical use, or are being considered toward practical use.
[Patent Document 1]
    JP 1992-269461 Unexamined Patent Publication (Kokai)[Patent Document 2]    JP 1993-36441 Unexamined Patent Publication (Kokai)[Patent Document 3]    JP 1998-144351 Unexamined Patent Publication (Kokai)[Patent Document 4]    JP 2000-138073 Unexamined Patent Publication (Kokai)[Patent Document 5]    JP 2001-6674 Unexamined Patent Publication (Kokai)[Patent Document 6]    JP 1992-238815 Unexamined Patent Publication (Kokai)[Patent Document 7]    JP 2002-25555 Unexamined Patent Publication (Kokai)[Non-Patent Document 1]    S. Hatake et al., “Journal of Power Sources”, (United States of America), Elsevier Science, 1997, Vol. 68, p. 416–420.[Non-Patent Document 2]    Preprint of the 27th Symposium on Solid State Ionics, Solid State Ionics, 2001, p. 34–35.[Non-Patent Document 3]    Preprint of the 41st Battery Symposium, the Electrochemical Society of Japan, the Committee of Battery Technology, 2000, p. 634–635.
However, several problems have been pointed out concerning with the secondary cells in which the insertion and elimination of Li+, F−, Mg2+ and H+ are utilized.
First, as for a secondary cell in which the insertion and elimination of F− and Mg2+ are utilized, up to the present time, an appropriate material for electrode or an appropriate material for electrolyte has not been found yet. Therefore, these have not achieved the stage where these can be practically used as a secondary cell.
Next, as for a secondary cell in which the insertion and elimination of Li+ are utilized, for example, when it is rapidly charged, there is a fear that Li not inserted completely is precipitated in a dendrite structure. The activity of this dendrite is very high. Thus, there is a fear that upon being exposed to the atmospheric air, the dendrite is reacted with oxygen in the atmospheric air, and the secondary cell does not exert the characteristics in a stable manner.
Furthermore, also in a secondary cell in which the insertion and elimination of H+ are utilized, when a hydrogen occlusion alloy that completely has occluded hydrogen is exposed to the atmospheric air, there is a fear that the hydrogen occlusion alloy generates hydrogen and reacts with oxygen in the atmospheric air, and the secondary cell does not exert the characteristics in a stable manner.
Moreover, as the all-solid-state secondary cell, a cell whose operation is surely recognized at present is only a cell in which lithium ion is used as movable ion. However, in an all-solid-state secondary cell in which lithium ion is used as movable ion, there are problems that a solid electrolyte inside of which Li ion moves at a high speed has not been found and the like. Furthermore, as a particularly serious problem, there is a problem of an interface between electrodes and an electrolyte. Namely, in an all-solid-state secondary cell in which lithium ion is employed as movable ion, it is required that Li ion can smoothly pass through the interface between electrodes and an electrolyte. However, actually, in this interface, another compound which does not transmit Li ion is formed at the time of charging and discharging reactions, and the problem that the charging and discharging reactions are hindered arises. For example, in the case where a complex oxide of Li and element A are employed for electrodes and a complex oxide of Li and element B are employed for an electrolyte, the complex oxide of element A and element B is generated at the interface between electrodes and the electrolyte and the transmission of Li ion is hindered.
Thus, there are a variety of problems concerning with the conventional secondary cells. Consequently, a secondary cell in which substances except for Li+, F−, Mg2+, and H+ are employed as movable ion has begun to be considered. However, a secondary cell which is stable and can withstand the practical use has not been found yet.